iOS: Apple doesn't allow apps to keep their home screen icons regularly updated with data—just notification badges for alerts and the like. Clever weather app Fahrenheit (which does, indeed, have a "Celsius" cousin) uses that notification badget to give you the temperature in degrees, no extra click needed.

Fahrenheit's actual app screen shows you all the stuff you'd expect: detailed conditions, forecasts, and the like. But it's the badge that's really appealing, as it uses the mechanism normally reserved for informing you of how many new messages or other pings are awaiting you to tally up the current temperature.

Fahrenheit (and its Celsius cousin) are 99 cents in the iTunes App Store, and are both designed for iPad as well as iPhone/iPod screens.